Syntax for Internet Hostnames

[Mark.Andrews at iengines.com]

	Foo.ex_ample.com is an illegal hostname.  B.T.W the is no
	such thing as "just the domain portion".  foo.ex_ample.com
	is a domain, as is ex_ample.com, as is com and as is ".".

	There is nothing intrisically wrong with ex_ample.com, it
	just can't legally contain, or be, a hostname or mail
	domain.  If you want it for some other use there is no
	reason not to delegate it.

	Mark

> Hello,
> 
> On the issue of legal characters for host names, would the underscore '_' be
> properly used in a domain name like ex_ample.com?  I can understand that some
> operating systems might have problem when encountering hostnames with
> underscores.  But would it be OK just for the domain name portion?  Or should
>  the
> hostname rule be applicable to all the labels in a name?  Internic seems to t
> reat
> underscore as a legal character as far as they are concerned.  Please advice.
> 
> Lawrence Chan
> lchan at montevino.com
> 
> Mark_Andrews at isc.org wrote:
> 
> > > I'm trying to find a simple explanation that describes the syntax of a le
> gal
> > > Internet host name.  I'm not a network administrator and found some of th
> e
> > > explanations in RFC 952 and 1123 to be confusing.
> >
> >         A hostname is composed of "A" - "Z", "a" - "z", "0" - "9", "-"
> >         and ".".  All other characters are illegal.  Hostnames are case
> >         insenitive.  e.g. "EXample.COM" == "EXAMPLE.com"
> >
> >         "." can only be used to seperate labels. In "example.com",
> >         "example" and "com" are labels.
> >
> >         "-" can only be used in the middle of a label, not at the start or
> >         the end of a label.  e.g. "host-20.example.com".  The following
> >         are illegal "-bad.example.com", "bad-.example.com", "-.example.com"
> .
> >
> >         A host name has to contain at least one letter.  This is currently
> >         enforced by not allowing all numeric top level domains.
> >
> >         Mark
> > >
> > > Thanks in advance!
> > >
> > > --
> > > Seabush
> > >
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> > >
> > >
> > --
> > Mark Andrews, Internet Software Consortium
> > 1 Seymour St., Dundas Valley, NSW 2117, Australia
> > PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org
> 
--
Mark Andrews, Internet Engines Inc. / Internet Software Consortium
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark.Andrews at iengines.com